1. Field of the Invention
The present invention relates to a tire mold in which parts for molding a tread are partitioned into a plurality of segments, and particularly to a technique of restricting protrusion of rubber into clearances between adjoining segments and of molding tires exhibiting superior uniformity.
2. Description of the Prior Art
In performing molding of pneumatic tires, sector partitioned mold in which parts for molding treads of tires are partitioned in a tire circumferential direction have been employed. The partitioned parts are called segments, and such segments are usually partitioned into 7 to 13 parts. When performing molding, each segment is moved inside in a radial direction toward a tire rotational axis whereupon the mold is closed for molding a tire. For instance, there is known a tire mold as disclosed in Japanese Patent Laid-Open Publication No. 2002-361632.
When performing molding, each segment moves in the tire radial direction. As illustrated in FIG. 1, when a segment 1a includes projecting streaks 2a, 2b for molding transverse grooves on a tread surface, the projecting streak 2a at a central portion of the segment 1a enters in a tire radial direction Ra from the surface of a green tire T for molding a transverse groove.
However, since the direction of the projecting steaks 2b at end portions of the segment 1a entering from the surface of the green tire T is identical to the direction Ra from which the projecting streak 2a enters, it is different from a direction Rb in which the projecting streaks 2b extend so that angular difference will be caused. As a result, the rubber of the green tire T will be pushed by the projecting streaks 2b from the central portion of the segment 1a towards the end portions. Similarly in the adjoining segment 1b, the projecting streaks 2d of the segment end portions will also enter from direction Rc, which is a direction different from an extending direction Rd thereof. As a result, the rubber of the green tire T will be pushed from the central portion of the segment 1b towards the end portions by the projecting streaks 2d. 
Accordingly, the volume of a portion pinched between the projecting streaks 2b and 2d of the green tire T will be increased. The portion where the volume is locally increased through the movement of the rubber will be pinched between adjoining segments in the course of closing the mold so that protrusion of rubber, which is called ‘flash’, is caused whereby the quality of external appearance is degraded. Moreover, the movement of the rubber will lead to an uneven thickness of the tread part which might cause degradations in tire performances.
For preventing such deficiencies of manufacture, there had been employed a method of preliminarily molding green tires having a smaller radius than an inner radius of the mold cavity. In such a case, the outer radius of the tire became large through the molding so that a framework of tires was grown in size which would lead to degradations in tire durability.